The invention disclosed herein pertains to a device for applying glue to labels in a container labeling machine.
A labeling machine should be able to apply labels of various configuration accurately on containers having various shapes. In their development, gluing devices have been adapted to account for use of various glues, differing qualities of labels and ever increasing working speeds. In any case, minimizing the glue consumption, accurate placement of the labels on the containers, good adhesion and lack of glue smearing are of great significance. Successful operation of gluing devices depends to a large extent on accurate control of the thickness of the film of glue on the roller with which pick-up elements for labels are contacted to transfer glue to them. Obtaining and maintaining optimal glue film thickness on the rollers has been achieved. This is done simply by holding the edge of a straight doctor blade or scraper close to the revolving glue transfer roller. The scraper is usually mounted on an axis that is parallel to the axis of the roller and that permits swinging the blade toward and away from the roller to obtain the desired glue thickness. A common practice is to have a threaded stud mounted in a fixed support such that the stud can be turned toward or away from the glue scraper and in contact with it in opposition to a spring for obtaining film thickness adjustment. A locknut is placed on the stud and it is tightened against the support when correct adjustment has finally been made. This traditional blade adjustment means results in much time being consumed in trying to establish the edge of the blade at the proper distance for obtaining the exact glue film thickness desired for the particular labels being used. Using a threaded stud provides no gauge as to whether the scraper is too close or too far from the roller, so usually iterative adjustment or adjustment by trial and error must be made. So there would be several attempts at adjustment before it was felt that the distance between the glue scraper and the roller was optimal for a majority of the labels being processed. Iterative adjustment procedures are not acceptable in high speed modern labeling machines.